The invention relates to a portable data carrier including a card-shaped or card-type body having a recess for receiving a chip module. The chip module includes at least one semiconductor chip on a first main side of a chip carrier connected to the card-shaped body, and a metallization layer disposed on a second main side of the chip carrier and having contact lugs.
Such portable data carriers are well known from the prior art. They are typically embodied in a card form (for example in the credit card format) with an incorporated integrated circuit module. The data carriers are then referred to as smart cards. Data carriers of the above-mentioned type are exposed to a wide variety of loads during use. Due to structural conditions with a card body and a chip module, high bending loads can act on the configuration and, depending on the structural layout, can lead to failures, caused for example by a chip fracture or the tearing of an electrical connection. The susceptibility of a configuration of that type is dependent on the chip size, on the length of a bonding wire connection between contact pads of a semiconductor chip and on the materials used.
A chip module known from the prior art usually has a carrier composed of epoxy resin. A semiconductor chip is applied on a first main side of the carrier. The chip is connected to the carrier, for example by adhesive bonding or lamination. A metallization layer is applied on a second main side of the carrier opposite to the first main side. The metallization layer has contact lugs and forms contacts of the chip module that are subsequently accessible externally. The metallization layer typically has six or eight contact lugs which are electrically isolated from one another and in each case are connected to contact pads of the semiconductor chip by bonding wires. In that case, the bonding wires are led through recesses in the carrier. A potting compound is applied on the first main side and surrounds the semiconductor chip and the bonding wires for mechanical protection of the semiconductor chip and of the bonding wires.
If the data carrier is exposed to bending loads, as occur for example in mail sorting installations during postal shipping, the data carrier can be damaged. The dictates of construction mean that a high kinetic energy acts there on the data carrier in a mail envelope. That energy is brought about on one hand by high speed and on the other hand by frequent changes in direction through movable rollers of the mail sorting installation.
In order to minimize the forces acting on the data carrier configuration, attempts have been made to divert the applied tensile and compressive forces to the adhesive connection between the chip module and the card-shaped body of the data carrier. That is done either by increasing the module bending resistance in the semiconductor chip and in the bonding wire region by using particularly hard coverings or by the use of reinforcement elements, for example frames on the first main side of the chip carrier. Based on good practical experience, there has been a shift toward using a so-called xe2x80x9chot-meltxe2x80x9d adhesive, for connecting the chip module to the card-shaped body, since that has proved to be particularly advantageous due to its elastic properties.
Nevertheless, damage to the semiconductor chip or the bonding wire connections in the chip module can occur in the event of high bending stresses.
It is accordingly an object of the invention to provide a portable data carrier which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which has a high reliability even in the event of high bending stresses.
With the foregoing and other objects in view there is provided, in accordance with the invention, a portable data carrier, comprising a card-shaped body having a recess formed therein and defining side edges. A chip module is to be disposed in the recess. The chip module has a chip carrier connected to the card-shaped body. The chip carrier has desired bending points located in a region within the side edges of the recess. The chip carrier has first and second main sides. The chip module has at least one semiconductor chip disposed on the first main side and a metallization layer disposed on the second main side. The metallization layer has contact lugs.
The invention is based on the insight that the flexure of the semiconductor chip or of the entire chip module becomes smaller as the dimensions of the chip module are made smaller. However, since the chip modules or portable data carrier configurations described in the introduction have to meet predetermined standards (ISO standard) it is not possible to arbitrarily reduce the size of the chip module. Therefore, the invention provides for the chip carrier to have desired bending points. Since, in principle, the weakest point yields in the event of bending stresses that occur, it is possible, through the use of a suitable configuration of the desired bending points in the chip carrier, to accommodate the semiconductor chip and the electrical connections (bonding wires) on an area that is resistant to bending. In other words, the invention thus provides for a stiff region of the chip module to be expanded in such a way that not only the semiconductor chip but also the wire bonding connections lie in the stiff region.
In accordance with another feature of the invention, the desired bending points are located in a region outside the semiconductor chip. It is even more advantageous if the desired bending points are disposed outside a covering surrounding the semiconductor chip. Since the desired bending points are simultaneously located in a region within the side edges of the recess, the forces acting on the portable data carrier can be kept away from the semiconductor chip and the electrical connections to the greatest possible extent.
In accordance with a further feature of the invention, the desired bending points are formed by at least one cutout in each contact lug of the metallization layer. The cutout subdivides the respective contact lug into a first and a second region. The at least one cutout in each contact lug weakens the metallization layer in this region which has the highest bending resistance of the entire chip module. The chip carrier itself, while being significantly thicker than the metallization layer, has a significantly lower bending resistance. As a result of this, the desired bending point sought is produced at the points of the cutout.
In accordance with an added feature of the invention, the first and second regions are connected to one another by at least one web. In this case, it is possible to refine the contact lugs by electroplating without modifying existing production tools or production cuts, which is a tried and tested and cost-effective method. If the cutout of the first and the second region were completely separated from one another, then the contact lugs would have to be refined by electroless plating.
In accordance with an additional feature of the invention, the cutouts run in a direction in the respective contact lugs in which the contact lugs lie adjacent one another. The cutouts of adjacent contact lugs lie on an axis in this case. This axis lies substantially parallel to the side edges of the semiconductor chip. Under no circumstances does it lead through the semiconductor chip. In that case, perforation of the semiconductor chip would be promoted.
In accordance with yet another feature of the invention, the respective webs have a significantly smaller width than the at least one cutout. The width of the web remaining in the contact lug substantially determines the bending resistance of the desired bending point. The minimum possible width of the web results from the electroplating requirements.
In accordance with a concomitant feature of the invention, as an alternative, the metallization layer could also end in a region within the desired bending points. This means nothing more than that the first region of the contact lug, which region is formed by the cutout, is obviated.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a portable data carrier, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.